1. Field of the Invention
The present invention relates to an upper tool removably attached to an upper tool holder device for a press brake, and more specifically to an upper tool which can actuate the upper tool holder device so that the clamping force can be increased when attached to the upper tool holder device.
2. Description of the Related Art
As is well known, the structure of a press brake is such that an upper table (referred to as an upper apron, sometimes) and a lower table (referred to as a lower apron, sometimes) are provided so as to be opposed vertically to each other and further any one of the upper and lower tables is moved up and down relative to the other as a ram.
Further, in the press brake, an upper tool is attached to the lower portion of the upper table and a lower tool is attached to the upper portion of the lower table.
In the above-mentioned structure, workpiece disposed between the upper and lower tools can be bent when both the tools are engaged with each other by moving the movable-side table up and down.
In the above-mentioned press brake, in order to exchange an upper tool with another upper tool according to the bending shape of workpiece, a number of upper tool holder devices are attached to the lower portion of the upper table, and further a number of tools are removably supported by a number of the upper tool holder devices, respectively.
Here, in the conventional upper tool holder device, an upper tool clamp is mounted on a holder body attached to the lower portion of the upper table, and the upper portion of the upper tool is strongly fastened and fixed between the holder body and the upper tool clamp when the upper clamp is fastened with fastening bolts.
In the conventional upper tool holder device, therefore, a great number of fastening bolts arranged on a number of upper tool holder devices must be rotated in order to exchange the upper tool on the upper table, thus causing a problem in that the tool exchange process is complicated and therefore troublesome.
To overcome the above-mentioned problem, another upper tool holder device has been so far proposed such that an air cylinder is attached for each upper tool holder device to fasten and unfasten the upper tool clamp with the use of the respective attached air cylinder.
In this conventional art upper tool holder device, however, since a number of air cylinders must be provided for a number of the upper tool holder devices independently, and further since an air source is required additionally, there exists another problem in that the structure is complicated and therefore the manufacturing cost thereof is high.
Further, in the conventional art upper tool holder device, whenever tile upper tool is unclamped by releasing the upper tool clamp provided for the upper tool holder device, there exists a danger that the released upper tool will fall down. Further, in the prior art upper tool holder device, during the upper tool setting work, since the upper tool must be first fastened slightly to such an extent that the upper tool will not fall and then the upper tool must be fastened strongly with the upper tool clamp after the alignment of both the upper and lower tools has been confirmed, there exists another problem in that the upper tool setting process is troublesome.
Further, there is another conventional art as disclosed in EP-0 387 121 A1 related to the present invention, whose structure is such that an upper tool is clamped between an upper tool holder body and an upper tool clamp pivotally attached to the upper table of a press brake. In this conventional structure, however, since the upper tool must be attached to and removed from the upper tool holder body by pivoting the upper tool about the pivotal axle of the upper tool clamp, there exists such a shortcoming that the shape of the upper tool is restricted.